Subj : MESO: Nws Weather Prediction Center College Park Md To : wx-storm@lists.illinois.edu From : COD Weather Processor Date : Tue Aug 12 2025 03:31:05 AWUS01 KWNH 120331 FFGMPD ILZ000-MOZ000-IAZ000-120900- Mesoscale Precipitation Discussion 0914 NWS Weather Prediction Center College Park MD 1130 PM EDT Mon Aug 11 2025 Areas affected...Northeast Missouri, Southeast Iowa, Western Illinois Concerning...Heavy rainfall...Flash flooding possible Valid 120329Z - 120900Z Summary...Showers and thunderstorms expanding across northern Missouri will lift slowly northeast overnight. Rainfall rates within this convection will reach 1-2"/hr, locally higher at times, resulting in 1-2" of rainfall. This may cause flash flooding. Discussion...The regional radar mosaic tonight shows an expanding area of showers and thunderstorms developing from north-central Missouri into southeast Iowa. This convection is blossoming in response to ascent driven by an overlap of modest height falls downstream of a shortwave trough axis positioned over Nebraska, and an MCV from remnant convection moving into southern Iowa. Downstream of these features, a S/SW LLJ at 850mb has been recently measured via local VWPs to be 15 kts, which is originating from a region of elevated thermodynamics sufficient to fuel heavy rain in thunderstorms. As this LLJ locally backs and accelerates downstream of the MCV, it will draw PWs as high as 2 inches, and MUCAPE above 2000 J/kg, northward, providing additional fuel for persistent convection within a WAA regime overnight. Rainfall rates as estimated via local radars have been generally modest so far at around 0.5-1"/hr. However, as the LLJ continues to strengthen it will not only resupply the more favorable thermodynamics northward, but also result in enhanced convergent ascent to drive stronger convection. During the next few hours, the CAMs, while mostly under-representing the current activity, suggest thunderstorms will become more widespread, and the HREF neighborhood probabilities indicate a 10-20% chance of 2"/hr rain rates developing, with brief rates to 3"/hr possible as shown by the 15-min HRRR rain accumulation. At the same time, while 0-6km mean winds will remain progressive to the northeast at 20-25 kts, sufficient bulk shear of 20-25 kts will help organize storms into clusters, coincident with Corfidi vectors collapsing to 5 kts or less and veering to the south. This indicates an increasing threat for backbuilding/training convection within the improving WAA. Although HREF 6-hr rainfall probabilities for 3" are modest at 10-15%, indicating that generally 1-2" of rain is likely with locally higher amounts, this may still be sufficient to cause rapid runoff. Not only will the rates be intense, but FFG is as low as 1.5-2"/3hrs for which the HREF exceedance probabilities peak around 20%. This is further evidence for the increasing flash flood risk overnight, with at least isolated instances possible in urban areas, over the more vulnerable soils, or where the most significant training can occur. Weiss ....Please see https://urldefense.com/v3/__http://www.wpc.ncep.noaa.gov__;!!= DZ3fjg!6-Wg4J8PPfQV0EfImKwv_a2YKq5N6tCvRJ74PlVn6hiQp2b993WAitry3AS8TcYfvmL-= UtafYSWDJjsPlnjvfC8K56w$ for graphic product... ATTN...WFO...DMX...DVN...EAX...ILX...LSX... ATTN...RFC...KRF...MSR...NWC... LAT...LON 42079071 41298973 40588957 39738995 39249075=20 39199086 38789174 38629258 38949335 39559371=20 40229386 40909354 41699259=20 =3D =3D =3D To unsubscribe from WX-STORM and you already have a login, go to https://lists.illinois.edu and use the "Unsubscribe" link. Otherwise email Chris Novy at cnovy@cox.net and ask to be removed from WX-STORM. --- SBBSecho 3.28-Linux * Origin: capitolcityonline.net * Telnet/SSH:2022/HTTP (1:2320/105) .